linux-kernel - Re: [syzbot] [mm?] WARNING in memory

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Message-ID: <7F95F86F-F002-4CD1-A5B2-4A261A9D1317@nvidia.com>
Date: Tue, 30 Sep 2025 22:13:20 -0400
From: Zi Yan <ziy@...dia.com>
To: syzbot <syzbot+e6367ea2fdab6ed46056@...kaller.appspotmail.com>,
 <syzkaller-bugs@...glegroups.com>
Cc: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>,
 David Hildenbrand <david@...hat.com>, Luis Chamberlain <mcgrof@...nel.org>,
 <akpm@...ux-foundation.org>, <linmiaohe@...wei.com>,
 <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
 <nao.horiguchi@...il.com>
Subject: Re: [syzbot] [mm?] WARNING in memory_failure

On 30 Sep 2025, at 21:51, Zi Yan wrote:

> On 29 Sep 2025, at 11:20, Zi Yan wrote:
>
>> On 29 Sep 2025, at 7:08, Pankaj Raghav (Samsung) wrote:
>>
>>>>
>>>> I want to change all the split functions in huge_mm.h and provide
>>>> mapping_min_folio_order() to try_folio_split() in truncate_inode_partial_folio().
>>>>
>>>> Something like below:
>>>>
>>>> 1. no split function will change the given order;
>>>> 2. __folio_split() will no longer give VM_WARN_ONCE when provided new_order
>>>> is smaller than mapping_min_folio_order().
>>>>
>>>> In this way, for an LBS folio that cannot be split to order 0, split
>>>> functions will return -EINVAL to tell caller that the folio cannot
>>>> be split. The caller is supposed to handle the split failure.
>>>
>>> IIUC, we will remove warn on once but just return -EINVAL in __folio_split()
>>> function if new_order < min_order like this:
>>> ...
>>> 		min_order = mapping_min_folio_order(folio->mapping);
>>> 		if (new_order < min_order) {
>>> -			VM_WARN_ONCE(1, "Cannot split mapped folio below min-order: %u",
>>> -				     min_order);
>>> 			ret = -EINVAL;
>>> 			goto out;
>>> 		}
>>> ...
>>>>
>>>> WDYT?
>>>>
>>> I think it should be fine as along as we return an error if someone is
>>> trying to split < min_order for file-backed folios.
>>>
>
> <snip>
>
>>
>> OK, I will send a proper patch to fix this. Thanks.

Let me try again:

#syz test: https://github.com/x-y-z/linux-dev.git fix_split_page_min_order-for-kernelci

--
Best Regards,
Yan, Zi